1. Field of the Invention
The present invention relates to a thin film transistor having an organic semiconductor film and a manufacturing method thereof. In addition, the present invention relates to a semiconductor device provided with the above thin film transistor and a manufacturing method thereof.
2. Description of the Related Art
A display device provided with thin film transistors (TFTs) has been studied recent years. The display device provided with TFTs can be operated in low-power consumption and occupy small space compared with CRT, therefore it has been used for a display portion of a personal computer, a PDA, or the like. These TFTs have been practically manufactured using inorganic semiconductor materials such as amorphous silicon, crystalline silicon, or the like. However, there is a problem that lots of effective substrate materials can""t be used since its processing temperature is above 350xc2x0 C. when TFTs are manufactured using inorganic semiconductor materials.
Consequently, in addition to the inorganic materials, a thin film transistor having an organic semiconductor film formed by organic materials (hereafter referred to as an organic TFT) has been researched. Since an organic TFT can be formed at low temperature, plastic materials can be used for the substrate. As a result, a light and flexible device can be obtained. Furthermore, the organic TFT has advantages of low production cost for the sake of being formed on the inexpensive substrate materials and low voltage for driving the device.
Dipping, casting, bar coating, spin coating, spraying, ink jetting or printing is applied for the organic semiconductor film which use a polymer type (high-molecular type) organic material. (For example, Japanese Patent Laid Open No.2000-29403, No.2000-269504). Also, vapor deposition or the like is applied for the organic semiconductor film which use a low-molecular type organic material. (For example, Japanese Patent Laid Open No. 8-228035, No.10-125924). In terms of improving uniformity in a film thickness, spin coating and vapor deposition are often used.
However, there have been problems that any of the above manufacturing methods requires a special apparatus, and that formed organic semiconductor films are so little to quantity consumed materials and most of the used materials are discarded in the end. Moreover, maintenance of apparatus such as cleaning of the inside of an apparatus cup or a chamber has needed to be continually performed in order to remove the contamination resulting from the material that is wastfully discarded. Therefore, a great cost for materials and man-hours for maintenance of apparatus have been required. As a result, it has not been desirable to apply these methods not only for the effect on the production cost, but also the disastrous effect on the environment generated from material wastes and liquid wastes.
It is difficult to coat the films separately by spin coating, so that patterning is required after coating the organic films allover. It is still difficult to perform patterning with absolute precision by this method. Also, there is a possibility of a thermal decomposition since temperature of sublimation is close to that of the thermal decomposition in some organic materials. In addition, ink jetting, printing and some other ways have not yet come into practical use.
Moreover, in the methods above, it is difficult to form a thin and uniform organic semiconductor film and to attain a TFIF characteristic.
An object of the present invention is to provide a method of manufacturing an organic semiconductor film that does not depend on an expensive and special apparatus and which can use a material efficiently. Another object of the present invention is to provide a method of manufacturing an organic TFT which is not influenced by the pyrolysis and which can simplify the manufacturing methods that need not a patterning process.
Further, another object of the present invention is to provide a method of manufacturing an organic semiconductor film, in which a thin and uniform organic semiconductor film can be formed.
In view of the above-mentioned problems, according to the present invention, it is characterized in that an organic semiconductor film is formed by a method that utilizes a phenomenon in which a solution is sucked into an aperture (hereinafter, simply referred to as injection method). That is, according to the present invention, a solution containing an organic semiconductor film material is injected into a spot (aperture) at which the organic semiconductor film is to be formed, and a solvent is then evaporated through drying, thereby the organic semiconductor film with thinness and uniformity is formed.
Specifically, a first substrate for forming an organic semiconductor film and a second substrate used for helping injection are superimposed on each other; an aperture is formed between the substrates with an insulating film formed at a specific spot; a part (including a corner portion), typically an end (hereinafter, simply referred to as end or edge) of both the substrates is immersed in a solution containing an organic semiconductor film material; and the organic semiconductor film material is injected into the aperture due to capillarity to form the uniform organic semiconductor film. Thus, an organic TFT is completed.
Further, it may be that: a first substrate for forming an organic semiconductor film and a second substrate used for helping injection are superimposed such that ends of both the substrates are not aligned with each other (an offset structure); an aperture is formed between both the substrates with an insulating film formed at a specific spot; a solution containing an organic semiconductor film material is dropped onto the ends of the substrates; and the solution is sucked into the aperture to carry out injection of the organic semiconductor film material to thereby form the uniform organic semiconductor film. Of course, it may be that: the substrates with the offset structure are immersed in the solution containing the organic semiconductor film material; and the organic semiconductor film material is injected into the aperture due to capillarity. Note that superimposition of both the substrates in such a manner that ends thereof are not aligned with each other means superimposition of both the substrates in such a manner that at least surfaces thereof on one side are shifted from each other. On the other hand, superimposition of both the substrates in such a manner that ends thereof are aligned with each other means superimposition of both the substrates in such a manner that at least surfaces thereof on one side are aligned with each other.
The insulating film formed at the above-described specific spot enables the formation of an organic semiconductor film with high controllability. Further, as described above, the insulating film also serves as a spacer that holds the aperture between the substrates, namely, an interval (gap). Note that it is sufficient that manufacturing of an organic semiconductor film in the present invention is performed at an atmospheric pressure or under an anaerobic atmosphere. Note that the anaerobic atmosphere indicates an atmosphere in which moisture and oxygen are eliminated, and indicates, for example, an inert gas atmosphere containing nitrogen, argon, or the like. Moreover, there may be adopted an atmosphere in which an inert gas is supplied to a reduced pressure atmosphere obtained once with the purpose of removing moisture and oxygen.
According to the present invention as described above, the semiconductor film with a very thin thickness (approximately several tens to 100 xc3x85) can be formed. Further, according to the present invention, the organic semiconductor film can be formed with efficiency, and thus, there is an expectation for simplification of the manufacturing process.
Further, according to the present invention, the organic semiconductor film can be formed only at the specific spot. Thus, apparatus maintenance and cost of cleaning solution and material can be eliminated, and therefore, total cost can be reduced. As a result, a low-cost semiconductor device provided with an organic TFT can be provided. Further, according to the present invention, there can be provided a method of manufacturing an organic semiconductor film, with which materials to be wasted and discarded are eliminated, with which liquid wastes along with apparatus maintenance and cleaning are not produced, and which is friendly to the environment.